In a case where a gasket made of a rubber-like elastic material is integrally molded to an outer edge portion of a metal separator for a fuel cell which serves as a metal plate, a rubber burr is generated in an outer peripheral portion of a molded product. As a result, a significant number of man hours are required for removing the burr. To offset this, there is a procedure according to the conventional art where resin frame 31 is integrally molded to an outer edge portion (a right end portion in the drawing) 22 of a metal separator 21, and then a gasket 41 made of a rubber-like elastic material is integrally molded to an inner side of the resin frame 31 (an inner peripheral side, a left side in the drawing) while setting the resin frame 31 to a dam portion against the rubber burr generation, as shown in FIG. 7.
According to this conventional procedure, however, there is a fear that the resin frame 31 will separate from the outer edge portion 22 of the metal separator 21 in a stage that the resin frame 31 is integrally molded to the outer edge portion 22 of the metal separator 21 (i.e., a stage that the gasket 41 made of the rubber-like elastic material is not molded yet) (a separation direction is shown by an arrow X).
In order to prevent the separation, it is thought that a concavo-convex shape 23 having a lot of concavities and convexities formed side by side should be provided to the outer edge portion 22 of the metal separator 21 such that when the resin frame 31 is integrally molded to the outer edge portion 22 of the metal separator 21 having the concavo-convex shape 23 (as shown in FIG. 8A) there is an increase of contact area between the metal separator 21 and the resin frame 31.
However, when the resin frame 31 is integrally molded to the outer edge portion 22 of the metal separator 21 having the concavo-convex shape 23, the metal separator 21 is set to a parting portion of a metal mold for molding the resin frame 31, and a resin molding material for molding the resin frame 31 is next injected into a metal mold cavity. Meanwhile, the metal separator 21 is an extremely thin plate because the fuel cell industry requires a compact structure for the fuel cell, and tends to be deformed (plastically deformed) by the application of an external force due to its thinness. Accordingly, in the molded product obtained by integrally molding the resin frame 31 to the outer edge portion 22 of the metal separator 21 having the concavo-convex shape 23, the outer edge portion 22 of the metal separator 21 should be buried in the middle in a thickness direction of the resin frame 31 in a normal situation without deformation of the outer edge portion 22 of the metal separator 21 as shown in FIG. 8B. The outer edge portion 22 of the metal separator 21, however, may be deformed under the influence of a resin molding material injecting pressure as shown in FIG. 8C. If a leading end 22a of the outer edge portion 22 is exposed to a surface in relation to the resin frame 31 as a result of deformation, there is a risk that an electric insulation, which is important in the fuel cell, is deteriorated.